Method of manufacturing nickel supports for oxide cathodes and cathodes provided with such supports



Sept. 25, 1962 H. MELSERT 3,056,061

METHOD OF MANUFACTURING NICKEL SUPPORTS FOR OXIDE CATHODES AND CATHODESPROVIDED WITH SUCH SUPPORTS Filed Jan. 18, 1960 lY/c/re/ .I/eeve B Oxidecoaizhg Era/H1219 surface 5 Passive IV! .Bound INVENTOR H. MELSERT AGEN.the supports of United States Patent Hans Melsert, Eindhoven,Netherlands, assignor to North American Philips Company, Inc., New York,N.Y., a corporation of Delaware Filed Jan. 18, 1960, Ser. No. 3,183Claims priority, application Netherlands Mar. 6, 1959 Claims. (Cl.313-346) It is known that the active nickel commonly used for oxidecathodes contains some impurities, inter alia magnesium, manganese,silicon, and iron, from which especially magnesium is favourable for theemission of electrons due to reduction of barium oxide. How ever,particularly magnesium has the disadvantage that it continuouslyevaporates from the cathode during opa mirror gives rise to acapacitance between the electrodes which becomes greater and greater.More particularly the resulting varying capacitance between the anodeand the control grid is very troublesome for the performance of thedevice of which the tube forms part.

This disadvantage may be avoided by the use of nickel of high purity,wherein the impurities are present in less than 0.022% by weight.However, such nickel brings about .a lower emission of electrons due tothe reduction The present invention permits of avoiding the troublesomeevaporation of magnesium from the cathode support without the electronemission being detrimentally affected.

According to the invention, for this purpose, in the tubular support foran oxide cathode, which support consists of nickel containing inter aliamagnesium as an im purity, steps are taken to ensure that, duringheating to from 1000 C. to 1200 C., oxygen can diffuse into the nickelfrom the surface opposite to the surface intended as the support for theemissive layer, until at least the magnesium present in the nickel hasbeen bound for the greater part, but not completely, by oxygen.magnesium remains free in the than half the wall thickness.

of the tubular support connected to tube means that communicate with theexterior of the oven chamber. The tube means may communicate with theoxygen contained in the surrounding air, or, in the alternative, for amore positive supply of oxygen for the dilfusion process the tube meansmay be connected to a gas circulating and/ or feeding system that pumpsoxygen to the tube means and tubular support. It has been found that, ifthe support has a wall thickness of 0.1 mm., heating at 1100 C., for aperiod of 20 minutes yields the desired result. The outer surface of thetube is kept in a neutral atmosphere such as nitrogen, for example, byfurnishing the interior of the oven chamher with a nitrogen atmosphere.The surface on which the electron-emissive material will be providedlater on is then still active since it still contains free magnesium,but it has been found that in the part of the support-wall in whichoxygen has penetrated, the magnesium is comis still present in theremaining part of the support-wall does not evaporate either.

Instead of being brought into contact with air, the said surface of thesupport with a wall thickness of 0.1 mm. may alternatively be coveredwith an oxide layer, for example a 0.1 mm. layer of nickel-oxide, fromwhich oxygen can be freed for heating at 1100" C. during 10 min. anddiffuse into the nickel in a neutral vacuo. This affords the advantagethat the said surface is insulated with respect to the heater of thecathode and that the heating process can coincide with the heatingcarried out for activating the electron-emissive layer after the cathodehas been mounted in a discharge tube. In fact, the temperature necessaryfor activating and disintegrating the emissive layer ordinarilyconsisting of equal parts barium oxide and strontium oxide, also liesbetween 1000 C., and 1200 C. In any case, the process of heating to thesaid temperature must not be continued until the Mg has been boundthroughout the whole Wall thickness. Free magnesium must always remainpresent at the surface covered with the oxide layer.

The content of impurities is low. The Mg-content of the said nickel is,for example, from 0.05 to 0.06% by weight. The nickel further maycontain 0.01% silicon; 0.02% iron and 0.101% manganese. However,impurities with a percentage of weight lower than 0.02% do not not reactnotably with the emitting oxides. Nickel containing such smallpercentages of impurities is therefore also said to be passive. From thesaid impurities only magnesium, and to a lesser degree also manganese,can give trouble due to evaporation.

In order that the invention may be readily carried into effect, it willnow be described, by way of example, with reference to the accompanyingdrawing showing one embodiment thereof, viz., a cathode sleeve, partlyin section, according to the invention.

In the FIGURE, a tubular sleeve 1 consisting of active nickel asmentioned above and having a wall thickness of 0.1 mm., is covered atthe outer side with an oxide coating 2 consisting of equal parts bariumcarbonate and strontium carbonate. The inner surface of the sleeve hasbeen covered with nickel oxide 3. During activation of the cathode inthe discharge tube, the sleeve 1 is heated at 1100 C. for 10 min.whereby the carbonates are converted into oxides and oxygen from the NiOlayer 3 difluses into the nickel of the sleeve 1, to about half itsthickness, thereby completely converting the Mg and, possibly the otherimpurities, into oxides, so that part 5 of the sleeve becomes passive.The remaining part 4 remains active. It is desirable that the part 5extends at least over half the wall thickness.

What is claimed is:

l. A method of manufacturing an oxide-coated cathode comprising thesteps of providing a nickel support containing magnesium as an impurity,said support havsecond surface and leave free the remaining portion ofsaid magnesium adjacent to said first surface.

2. A method of manufacturing an oxide-coated cathode comprising thesteps of providing a nickel support containing magnesium as an impurity,said support havpredetermined part of said distance to cause asubstansaid magnesium to become bound with said oxygen adjacent to saidsecond surface and leave free the remaining portion of said magnesiumadjacent to said first surface.

3. A method according to claim 2 wherein said nickel support comprises atubular member having a lateral wall, said first and second surfacescomprising the interior an exterior surfaces, respectively, of saidwall, and during said heating step said oxygen passes through theinterior of said tubular member for said diffusion thereof and saidfirst surface is maintained in a neutral .atmosphere.

4. A method according to claim 3 wherein during said heating step saidsupport is heated from 1000 C. to 1200 C.

5. A method according to claim 3 heating step said support is heated atminutes.

6. A method according to claim 2, wherein said oxygen binds saidmagnesium adjacent to said second surface greater than one-half of saiddistance.

7. A method according to claim 2 further compris ing the step ofcovering said second surface with an oxide layer prior to said heatingof said support to provide said oxygen for said diffusion.

8. A method according to claim 7 wherein said first surface is coveredwith said alkaline earth oxide prior to said heating, and said supportis effected in a vacuum to provide simultaneously the aforesaiddiffusion and emiswherein during said 1100 C. for twenty sive activationof said alkaline earth oxide of said first surface.

9. A nickel support containing magnesium as an impurity for supportingan electron emissive layer of an oxide-coated cathode comprising a firstsurface for support of an alkaline earth oxide, and a second lateralsurface disposed a predetermined distance from said first surface, asubstantial portion of the magnesium being bound adjacent to said secondsurface and the remaining portion thereof free adjacent to said firstsurface.

10. A nickel support containing magnesium as an impurity for supportingan electron emissive layer of an oxide-coated cathode comprising ahollow cylinder with a lateral wall having a predetermined thickness,said lateral wall having a first surface to support said emissive layer,and a second surface, a substantial portion of the magnesium being boundadjacent to said second surface and the remaining portion thereof beingfree adjacent to said first surface.

References Cited in the file of this patent UNITED STATES PATENTS2,778,970 Widell Jan. 22, 1957 2,912,611 Beck Nov. 10, 1959 FOREIGNPATENTS 213,179 Australia Feb. 7, 1957

9. A NICKEL SUPPORT CONTAINING MAGNESIUM AS AN IMPURITY FOR SUPPORTINGAN ELECTRON EMISSIVE LAYER OF AN OXIDE-COATED CATHODE COMPRISING A FIRSTSURFACE FOR SUPPORT OF AN ALKALINE EARTH OXIDE, AND A SECOND LATERALSURFACE DISPOSED A PREDETERMINED DISTANCE FROM SAID FIRST SURFACE, ASUBSTANTIAL PORTION OF THE MAGNESIUM BEING BOUND ADJACENT TO SAID SECONDSURFACE AND THE REMAINING PORTION THEREOF FREE ADJACENT TO SAID FIRSTSURFACE.